This application claims the benefit of a Japanese Patent Application No. 2004-171209 filed Jun. 9, 2004, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to head position control methods and disk apparatuses, and more particularly to a disk position control suited for application to a seek that is carried out in a case where a track (or cylinder) prescribed by servo information recorded on a disk is deviated from a circular locus scanned by a head within a disk apparatus loaded with the disk due to eccentricity of the disk, and to a disk apparatus employing such a head position control method.
2. Description of the Related Art
For example, concentric tracks are formed on a magnetic disk that is used in a magnetic disk apparatus such as a hard disk drive (HDD), and each track is sectioned into a plurality of sectors in a peripheral direction of the magnetic disk. Data recording on the magnetic disk is carried out in units of sectors. Servo information includes information (track number) for identifying the track and information (sector number) for identifying the sector, and this servo information is recorded together with the data in the case of the magnetic disk employing a data surface servo system that records both the data and the servo information on the same surface of the magnetic disk.
Conventionally, the forming of the track and the recording of the servo information are carried out in a state where the magnetic disk is loaded into the magnetic disk apparatus. This recording of the servo information on the magnetic disk is also sometimes referred to as a self-Servo Track Writer (self-STW). For this reason, the tracks are formed concentrically about a rotary axis of the magnetic disk. However, when forming the track on the magnetic disk, the magnetic disk and the magnetic head vibrate, and the track does not become a true circle due to the vibration. Accordingly, there is a possibility that mutually adjacent tracks will interfere with each other due to the vibration, and there is a limit to reducing the track pitch, thereby making it difficult to improve the recording density of the magnetic disk. Moreover, since the servo information is recorded with respect to the magnetic disk that has been loaded into each magnetic disk apparatus, it is difficult to improve the productivity.
On the other hand, the Servo Track Writer (STW), which is a high-precision apparatus exclusively for writing, is recently used for forming the track and recording the servo information with respect to the magnetic disk. The STW forms the track and records the servo information with respect to a large number of magnetic disks, and each magnetic disk formed with the track and recorded with the servo information is then loaded into the individual magnetic disk apparatus. By use of the STW, it is possible to reduce the track pitch and improve the recording density of the magnetic disk. In addition, since the forming of the track and the recording of the servo information are carried out with respect to the large number of magnetic disks by the STW, the productivity can also be improved. Recording the servo information on the magnetic disks in such a manner by use of the STW is sometimes also referred to as “stack STW”, and in the following description, an apparatus which carries out the stack STW will be referred to as a “stack STW”.
But when using the stack STW, the track is formed about the rotary axis of the magnetic disk within the stack STW. Hence, when the magnetic disk is loaded into the magnetic disk apparatus, the center of the track does not completely match the rotary axis of the magnetic disk within the magnetic disk apparatus, and eccentricity occurs. This eccentricity mainly includes a first order component that is generated due to the difference between the center of rotation of the magnetic disk within the STW and the center of rotation of the same magnetic disk within the magnetic disk apparatus, but also includes high order components. For this reason, when carrying out a seek in the magnetic disk apparatus, it is necessary to control the position of the magnetic head so as to scan a virtual circular locus approximately matching the track, by carrying out a correction that follows and corrects the eccentricity or neglects the eccentricity.
It is possible to control the position of the magnetic head while measuring an amount of the eccentricity and a phase of the eccentricity (angular direction of the eccentricity), but in this case, a high-speed computation process must be performed to calculate a correction quantity from the amount and the phase of the eccentricity, and the amount of the eccentricity may greatly change temporarily due to shock applied to the magnetic disk apparatus or the like. Consequently, such a real-time control has a slow response and is unsuited for a high-speed seek.
The measurement of the amount and the phase of the eccentricity may be carried out in a state where the magnetic disk is loaded into the magnetic disk apparatus, as one kind of tuning that is carried out when shipping the magnetic disk apparatus, for example. A Japanese Laid-Open Patent Application No. 9-330571 proposes storing the amount and the phase of the eccentricity measured at the time of the tuning or, the correction quantity that is calculated from the amount and the phase of the measured eccentricity, in a nonvolatile memory within the magnetic disk apparatus, and controlling the position of the magnetic head during the seek based on the stored amount and phase of the eccentricity or the stored correction quantity. When controlling the position of the magnetic head during the seek based on the amount and the phase of the eccentricity or the correction quantity stored in the nonvolatile memory, the position of the magnetic head is first fixed so as to access a specific track (or cylinder) on the magnetic disk. Based on the servo information read from the specific track (or cylinder), the amount and the phase of the eccentricity or the correction quantity corresponding to the track number and the sector number within the servo information are read from the nonvolatile memory. The eccentricity of the magnetic disk within the magnetic disk apparatus is corrected based on the correction quantity that is calculated from the read amount and phase of the eccentricity or from the read correction quantity, by controlling the position of the magnetic head so as to scan a virtual circular locus approximately matching the track.
However, when storing the amount and phase of the eccentricity or the correction quantity in the nonvolatile memory within the magnetic disk apparatus, the cost of the magnetic disk apparatus increases by an amount required to provide the nonvolatile memory within the magnetic disk apparatus. In addition, when the nonvolatile memory is mounted on a Printed Circuit Board (PCB), the information necessary to correct the eccentricity of the magnetic disk is lost if the PCB is replaced due to a failure or the like of other parts mounted on the PCB. Because the information necessary to correct the eccentricity of the magnetic disk differs for each individual magnetic disk apparatus, if the PCB is replaced by a new PCB, it becomes necessary to again measure the amount and phase of the eccentricity or, calculate the correction quantity therefrom, and to store the amount and phase of the eccentricity or the calculated correction quantity into the nonvolatile memory of the new PCB.